Thanks for the suggestion Cat_7. I tried build 143 again with the same result; I think I have a clue about what is happening...
There are some small differences between the Mac OS 8-bit color palette and Windows, in particular shades of grey, which are used abundantly in Escape Velocity.
Interestingly, I took a screenshot from within Mac OS 7.5.5 while full-screen with Basilisk II. When I opened the screenshot in Windows, it looked perfect. But while I was taking the screenshot, it was displaying the (inaccurate) Windows palette as seen below. So the emulator seems to be working perfectly in this regard.
Here is an example of what I'm seeing:
I am thinking this is not correctable, but tell me if I'm wrong.